metamorphic
Quartzite
Metamorphic rock predominantly composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but yellow/brown when stained by iron oxides; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none, breaks with conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but yellow/brown when stained by iron oxides; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none, breaks with conchoidal or irregular fracture.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together into a dense, hard rock. Can range from Proterozoic to more recent geological ages.
Uses & applications
Used as a decorative stone in construction, road ballast, manufacture of silica glass, and as a durable raw material for stone tools or flooring.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains themselves rather than around the grain boundaries as sandstone does. It is one of the most resistant rocks to physical and chemical weathering.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and lack of reaction to acid. It often appears sugary or crystalline on fresh breaks. It is commonly found in mountain ranges or old cratons worldwide.
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